In the art of noise control mufflers of the type which are commonly attached to air actuated devices such as air motors, cylinders and the like, there have been various types of mufflers either constructed or proposed for absorbing or controlling the noise of the exhaust air from the device. Some muffles incorporate a plurality of screens or perforated sheets having fine holes which restrict the flow of exhaust air. Other mufflers incorporate elements which define long tubular passages arranged in a manner to form long decelerating paths for the exhaust air. Another type of an air exhaust muffler, for example, as disclosed in U.S. Pat. No. 3,374,855, incorporated an open cell expanded foam material to define small or microscopic holes or passages for the exhaust air.
A common problem in air exhaust mufflers or the types described above is the problem caused by the small passages or holes becoming clogged from the compressed air line contaminates such as dirt, dust particles and gummy oil. Such clogging of the passages or holes produces a restriction to the flow of air, thereby decreasing the pressure drop across the air actuated device. Sometimes such a decrease in the pressure drop causes the device to become less efficient or operate in an undesirable manner.